A control device of an internal combustion engine is described in the Patent Document 1.
The engine of the Document 1 comprises fuel injectors, an air flow meter and an air-fuel ratio sensor.
The injector injects a fuel when a command corresponding to a target fuel injection amount (hereinafter, this command will be referred to as—fuel injection command—) is given to the injector. In the case that the injector can inject the fuel of the amount corresponding to the command exactly, that is, the injector has no error, the fuel of the amount corresponding to the target amount is injected from the injector.
The air flow meter outputs an output value corresponding to an amount of an air flowing therethrough (hereinafter, this amount will be referred to as—fresh air amount—).
The control device calculates the fresh air amount on the basis of the output value of the air flow meter. That is, the air flow meter detects the fresh air amount. In the case that the air flow meter can output an output value exactly corresponding to the actual fresh air amount, that is, the air flow meter has no error, the fresh air amount is exactly calculated on the basis of the output value of the air flow meter. That is, the air flow meter exactly detects the fresh air amount.
The air-fuel ratio sensor outputs an output value corresponding to an air-fuel ratio of a mixture gas formed in the combustion chamber of the engine (i.e. a gas of a mixed air and fuel and hereinafter, this gas will be referred simply to as—mixture gas—).
The control device calculates the air-fuel ratio of the mixture gas on the basis of the output value of the air-fuel ratio sensor. That is, the air-fuel ratio sensor detects the air-fuel ratio of the mixture gas.
In the case that the injector and the air flow meter have no error, the air-fuel ratio of the mixture gas calculated (hereinafter, this ratio will be referred to as—estimated air-fuel ratio—) from the fuel injection amount corresponding to the fuel injection command and the fresh air amount detected by the air flow meter (hereinafter, this amount will be referred to as—detected fresh air amount) corresponds to the air-fuel ratio of the mixture gas detected by the air-fuel ratio sensor (hereinafter, this ratio will be referred to as—detected air-fuel ratio—).
In other words, in the case that the injector or the air flow meter has an error, the estimated air-fuel ratio may become corresponding to the detected air-fuel ratio incidentally, however, in many cases, the estimated air-fuel ratio does not become corresponding to the detected air-fuel ratio.
Therefore, in the case that the estimated air-fuel ratio does not correspond to the detected air-fuel ratio, it can be judged that the injector or the air flow meter has an error.
There is a control using the fuel injection amount understood from the fuel injection command (hereinafter, this amount will be referred to as—commanded fuel injection amount—) or detected fresh air amount as an engine control.
If the injector has no error, the desired object of this control can be accomplished even when this control is performed using the commanded fuel injection amount itself or if the air flow meter has no error, the desired object of this control can be accomplished even when this control is performed using the detected fresh air amount itself.
However, in the case that the injector has an error, when the control is performed using the commanded fuel injection amount itself, the desired object of this control is not accomplished and in the case that the air flow meter has an error, when the control is performed using the detected fresh air amount itself, the desired object of this control is not accomplished.
Therefore, in order to accomplish the desired object of each control, when the injector has an error, the control should be performed using the commanded fuel injection amount appropriately corrected and when the air flow meter has an error, the control should be performed using the detected fresh air appropriately corrected.
That is, when the estimated air-fuel ratio does not correspond to the detected air-fuel ratio, it can be judged that the injector or the air flow meter has an error and therefore, the commanded fuel injection amount or the detected fresh air amount should be corrected.
In the device of the Document 1, when the estimated air-fuel ratio does not correspond to the detected air-fuel ratio, the commanded fuel injection amount and the detected fresh air amount are corrected as follows.
In the device of the Document 1, a ratio of the estimated air-fuel ratio relative to the detected air-fuel ratio (i.e. the estimated air-fuel ratio/detected air-fuel ratio and hereinafter, this will be referred to as—air-fuel-ratio —) is calculated during the engine operation.
Then, when the estimated air-fuel ratio corresponds to the detected air-fuel ratio, the air-fuel-ratio is “1” and therefore, a value is calculated by subtracting “1” from the air-fuel-ratio calculated in the case that the estimated air-fuel ratio does not correspond to the detected air-fuel ratio (=the ratio of the air-fuel ratio−1 and hereinafter, this value will be referred to as—air-fuel ratio difference—).
On the other hand, influences of the fuel injection difference and the fresh air amount detection difference maximally given to the air-fuel ratio difference are obtained by an experience, etc. and a rate of the air-fuel ratio difference due to the fuel injection difference in the air-fuel ratio (this rate is smaller than “1” and hereinafter, will be referred to as—fuel injection difference proportion) and a rate of the air-fuel ratio difference due to the fresh air amount detection difference (this rate is smaller than “1” and will be referred to as—fresh air amount detection difference proportion—) are previously obtained.
The sum of the fuel injection and fresh air amount detection difference proportions (=the fuel injection difference proportion+the fresh air amount detection difference proportion) is “1”.
In the device of the Document 1, the fuel injection difference rate is calculated by multiplying the air-fuel ratio difference calculated during the engine operation by the fuel injection difference proportion (=the air-fuel ratio difference×the fuel injection difference proportion) and the fresh air amount detection difference rate is calculated by multiplying the air-fuel ratio difference calculated during the engine operation by the fresh air amount detection difference proportion (=the air-fuel ratio difference×the fresh air amount detection difference proportion).
When the air-fuel-ratio is larger than “1”, the estimated air-fuel ratio is larger than the detected air-fuel ratio, that is, the estimated air-fuel ratio is leaner than the detected air-fuel ratio and therefore, it can be understood that the amount of the fuel injected actually from the injector (hereinafter, this amount will be referred to as—actual fuel injection amount—) is smaller than the commanded fuel injection amount and the actual fresh air amount is larger than the detected fresh air amount.
In this case, it is necessary to correct the fuel injection command corresponding to the target fuel injection amount so as to increase the command in order to make the injector inject the fuel of the amount corresponding to the target amount and it is necessary to correct the detected fresh air amount so as to increase the amount in order to detect the actual fresh air amount on the basis of the output value of the air flow meter.
In the device of the Document 1, the fuel injection command is corrected by multiplying this command by a value obtained by adding the fuel injection difference rate to “1” (=the fuel injection command×(1+the fuel injection difference rate)) and the detected fresh air amount is corrected by multiplying this amount by a value obtained by adding the fresh air amount detection difference rate to “1” (=the detected fresh air amount×(1+the fresh air amount detection difference rate)).
When the air-fuel-ratio is smaller than “1”, the estimated air-fuel ratio is smaller than the detected air-fuel ratio, that is, the estimated air-fuel ratio is richer than the detected air-fuel ratio and therefore, it can be understood that the actual fuel injection amount is larger than the commanded fuel injection amount and the actual fresh air amount is smaller than the detected fresh air amount.
In this case, it is necessary to correct the fuel injection command corresponding to the target fuel injection amount so as to decrease this command in order to make the injector inject the fuel of the amount corresponding to the target fuel injection amount and it is necessary to correct the detected fresh air amount so as to decrease this amount in order to detect the actual fresh air amount on the basis of the output value of the air flow meter.
In the device of the Document 1, the fuel injection command is corrected by multiplying this command by a value obtained by subtracting the fuel injection difference rate from “1” (=the fuel injection command×(1−the fuel injection difference rate)) and the detected fresh air amount is corrected by multiplying this amount by a value obtained by the fresh air amount detection difference rate from “1” (=the detected fresh air amount×(1−the fresh air amount detection rate)).